Tunnels play a critical role in the ongoing delivery and maintenance of the infrastructure required to support our modern world. Design and construction of tunnels present some of the most daunting challenges in the geoengineering field. Tunnel engineering is used in design and construction of tunnels in urban as well as remote areas. Tunneling often presents situations requiring technical skills, commitment and practical knowledge, in order to achieve a successful project outcome.
What is tunnel engineering?
Tunnel engineering isn’t just a standalone service. It encompasses various aspects and functions of mechanical, electrical, geotechnical and civil engineering for a range of underground projects. Advanced 2D/3D continuum as well as discontinued computer modeling, practical and traditional design methods are used to achieve project objectives. Tunnel engineering provides services for every stage of the life cycle of a tunneling project such as:
• Asset Management
Tunnel engineering services are used in projects such as:
• TBM bored tunnels- These are tunnels in congested urban areas for utilities, road and rail networks .
• Subaqueous tunnels- For crossing of very deep waterways.
• Immersed tunnels- For the crossing of channel type waterways, rivers and harbor basins. These are typically alternatives to a bridge crossing to provide unobstructed navigation.
• Long tunnels-Built under mountainous regions.
• Cut & cover tunnels- Shallow tunnels built in urban areas that have moderate surface constraints. These could be approaches to immersed or bored tunnels.
• Rock & CL tunnels- Structures with varying/irregular cross-section shape. These are generally shorter tunnels under deep waters or mountains where it isn’t financially feasible to undertake TBM bored tunnel construction.
What’s involved in tunnel engineering?
● Pre-bid geotechnical evaluations
● Contract documents evaluations
● Excavation staging & support design
● Cost estimating
● Tunnel & shaft design
● Value engineering
● Ground modification design
● Structural geologic mapping/evaluation
● Geotechnical instrumentation & monitoring
● Claims analysis & support
In addition, there are a number of aspects that are an integral part of tunnel engineering projects such as:
• Construction inspection
• Contract management
• Resident engineer services
● Construction claims analysis
• Submittal review
• Selection of the trenchless methods & equipment
• Assessment or characterization of existing geotechnical conditions
• Jacking or receiving the pit design
• Preparation of geotechnical contract documentation
Inspection & Rehabilitation
● Evaluation of existing ground structure and support
• Facility inspection
● Evaluation of the existing groundwater and geotechnical conditions
● Preparation of alternatives for rehabilitation design
● Development of ventilation and re-entry safety procedures
What is a Tunnel Engineer?
A skilled tunnel engineer is an experienced designer who handlesall engineering tasks for construction of tunnels as well as other connected underground structures. They provide practical tunnel designs that minimize risks and help reduce construction costs.
Tunnel design presents a number of complex technical challenges and an expert tunneling engineer applies a multidisciplinary and collaborative approach to multiple tunnel types used for transportation, wastewater, water as well as hydroelectric projects. They also help with risk management procedures as well as collaboration with different teams involved in the projects. A tunneling engineer provides a rangeof solutions, such as:
For owners and engineering teams
● Feasibility studies and evaluation of alternatives.
● Geotechnical evaluations for various underground projects.
● Co-ordinated detailed design calculation, specifications, drawings, and designing of geotechnical contract documents for shafts, tunnels as well as geotechnical instrumentation.
● Cost estimationfor the project.
● Management of risk factors in the design and tunnel construction.
● Construction management.
● Inspection functions.
● Rehabilitation designs for an existing tunnel.
● Emergency response and problem analysis.
● Remedial action plan and design.
● Claims review, expert witness work and cost analysis.
For private and municipal contractors
● Pre-bid evaluation of contract specifications and geotechnical bid documents
● Excavation support design & submittals
● Siting and feasibility studies
● Tunnel support design &submittals
● Value engineering change proposals
● Geo-technical instrumentation design&submittals
● Claims support
Other general tunnel engineering tasks
• Siting& feasibility studies- these include geotechnical exploration and lab-testing programs
• Estimates at all the project development stages
• Evaluation of designs for constructability
• Initial ground support for tunnels as well as shafts
• Grouting & ground improvement design
• Preliminary & final design
• Precast concrete segmental lining
• Preparation of contractual documents (plans, specs, etc)
• Numerical modeling
In addition to all these tasks, tunnel engineers could also be involved in risk management aspects such as:
● Qualitative risk analysis
● Risk register development
● Tracking & verification of mitigation measures
● Probabilistic quantitative analysis of scheduling costs and scheduling impacts
● Budget &schedule contingency analysis
Systems and tools that tunnel engineers use
Tunnels and variousrelated infrastructure provide solid underground connections for rail, road, and highwaytransit systems. Their scale, application and complexity demand various specialized geotechnical technologies that work in tandem with tunnel surveying, analysis and design tools such as:
• Automatic 3D & distance measurement systems
• Reflectors & marking material
• Settlement measurement systems
• Tunnel laser scanner systems
• Guidance systems for TBMs &roadheaders
• Motorlaser systems for detailed NATM tunneling
• Inclinometers & tilt sensors
• Extensometers and crack meters
In addition to these, systems such as pressure cells, strain meters, anchor load cells and measuring anchors, water level sensors, piezometers and vibration and acoustic emission sensors; dedicated surveying software,and fully-integrated tunnel information systems are used in tunnel engineering projects.
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